Semiconductor memory device having stacked word lines and conductive pillar

ABSTRACT

According to one embodiment, a manufacturing method of a semiconductor memory device includes forming a stacked body in which word line material layers and insulating layers are alternately stacked on a base layer. The method includes forming first holes on the stacked body so as to be arranged in a first direction and in a second direction that intersects with the first direction. The method includes forming resistance-change films on inner walls of the first holes, forming bit lines inside the resistance-change films in the first holes, and dividing the stacked body in the first direction by forming second holes so that a portion in the stacked body adjacent to the resistance-change films in the second direction. The method includes forming inter-bit line insulating films in the second holes.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a division of and claims the benefit of priorityunder 35 U.S.C. §120 from Ser. No. 14/748,335 filed Jun. 24, 2015, whichis a division of U.S. Ser. No. 14/023,865 filed Sep. 11, 2013 (now U.S.Pat. No. 9,099,648 issued Aug. 4, 2015) and claims the benefit ofpriority of U.S. Provisional Patent Application 61/818,643 filed May 2,2013; the entire contents of each of which are incorporated herein byreference.

FIELD

Embodiments described herein relate generally to a method formanufacturing a semiconductor memory device and the semiconductor memorydevice.

BACKGROUND

A resistance random access memory that has a structure that laminatesword line array layers including line-shaped word lines, provides bitlines in pillar shapes in a stacking direction, and providesresistance-change films between the word lines and the bit lines isbeing proposed.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic perspective view showing an example of a memorycell array of a semiconductor memory device of an embodiment;

FIG. 2 is a schematic plan view showing an example of the memory cellarray of the semiconductor memory device of the embodiment;

FIG. 3 is an A-A′ cross sectional view of FIG. 2; and

FIG. 4A to FIG. 11B are schematic plan views showing method formanufacturing the semiconductor memory devices of the embodiments.

DETAILED DESCRIPTION

According to one embodiment, a manufacturing method of a semiconductormemory device is disclosed. The method can include forming a stackedbody in which word line material layers and insulating layers arealternately stacked on a base layer. The method can include formingfirst holes on the stacked body so as to be arranged in a firstdirection and in a second direction that intersects with the firstdirection. The method can include forming resistance-change films oninner walls of the first holes. The method can include forming bit linesinside the resistance-change films in the first holes. The method caninclude dividing the stacked body in the first direction by formingsecond holes so that a portion in the stacked body adjacent to theresistance-change films in the second direction. In addition, the methodcan include forming inter-bit line insulating films in the second holes.

Hereinbelow, embodiments will be described with reference to thedrawings. Note that, in the drawings, same reference signs are given tosame elements.

FIG. 1 is a schematic perspective view illustrating an example of amemory cell array of a semiconductor memory device of an embodiment. InFIG. 1, illustration of insulating films between respective wires isomitted.

FIG. 2 is a schematic plan view illustrating the example of the memorycell array illustrated in FIG. 1. FIG. 2 corresponds to a cross sectionthat is parallel to an XZ plane in FIG. 1.

FIG. 3 is an A-A′ cross sectional view of FIG. 2.

Global bit lines GBL are provided on a substrate via insulating layers(all of which are not illustrated). The global bit lines GBL extend inan X direction (first direction). The plurality of global bit lines GBLis aligned in a Y direction (second direction) via inter-wire insulatingfilms that are not illustrated. The global bit lines GBL are formed forexample of a metal material.

The X direction and the Y direction intersect orthogonally in a planethat is parallel to a main surface of the substrate. Further, adirection that is vertical to the main surface of the substrate andintersects orthogonally to the X direction and the Y direction will betermed a Z direction (third direction).

As illustrated in FIG. 3, interlayer insulating films 11 are provided onthe global bit lines GBL. The interlayer insulating films 11 are forexample silicon oxide films.

Select gate lines SG are provided on the interlayer insulating films 11.The select gate lines SG are for example titanium nitride films.Alternatively, the select gate lines SG may be silicon films to whichimpurities are added and that have conductivity.

As illustrated in FIG. 1, the select gate lines SG extend in the Ydirection. The select gate lines SG are aligned in the X direction.

Channel bodies 14 are provided via conductive layers 13 on the globalbit lines GBL. Conductive layers 15 are provided on the channel bodies14.

The conductive layers 13, the channel bodies 14, and the conductivelayers 15 are formed of, for example, polysilicon layers. The conductivelayers 13 and the conductive layers 15 contain higher concentration ofthe impurities than the channel bodies 14.

Laminate bodies of the conductive layers 13, the channel bodies 14, andthe conductive layers 15 are formed in pillar shapes, and are arrangedon the plurality of global bit lines GBL in a matrix shape.

Gate insulating films 16 are provided between the channel bodies 14 andthe select gate lines SG.

The select gate lines SG that are adjacent in the X direction sandwicheach channel body 14 via the gate insulating films 16.

Interlayer insulating films 12 as illustrated in FIG. 3 are provided onthe select gate lines SG.

A stacked body to be described later is provided on each interlayerinsulating film 12.

As illustrated in FIG. 3, insulating layers 20 are provided oninterlayer insulating film 12. The insulating layers 20 are formed of,for example, silicon oxide films.

Plural layers of word lines WL are stacked on insulating layers(insulating layers of the lowest layer) 20. Word lines WL are arrangedcorresponding to a number of the select gate lines SG in the X directionin each layer. The word lines WL extend in the Y direction. Theinsulating layers 20 are provided between the word lines WL in differentlayers.

Bit lines BL formed of a pillar-shaped metal material are provided onthe conductive layers 15. The bit lines BL are arranged in a matrixshape in the X direction and Y direction.

The bit lines BL are aligned in the Y direction between the word linesWL that are adjacent in the X direction. Inter-bit line insulating films21 as illustrated in FIG. 6B are provided between the bit lines BL thatare adjacent in the Y direction. The inter-bit line insulating films 21are provided in pillar shapes extending in the Z direction (thirddirection), similar to the bit lines BL.

Selecting elements are arranged between the bit lines BL and the globalbit lines GBL. Here, the selecting elements include the gate insulatingfilms 16, the conductive layers 13, 15, the channel bodies 14, and theselect gates SG.

Resistance-change films 30 are provided between the bit lines BL and theword lines WL. The resistance-change films 30 are provided on both sidewalls in the X direction of the bit lines BL. The word lines WL that areadjacent in the X direction sandwich the bit lines BL via theresistance-change films 30.

As illustrated in FIG. 2, every other ones in the X direction of theword lines WL are connected to a common line, and are given the samevoltage.

When a selecting element is turned on by a potential given to a selectgate line SG, a bit line BL electronically connects to a global bit lineGBL. That is, the selecting element selects a bit line BL that is aselected target.

The selecting element including the select gate line SG, the gateinsulating films 16, and the channel body 14 selects a bit line BL to beactivated.

The resistance-change films 30 can be electrically switched between astate in which a resistance is relatively low (set state) and a state inwhich the resistance is high (reset state), and store data in anon-volatile manner.

The resistance-change films 30 in the high resistance state transitionto the low resistance state when a voltage of a certain value or more isapplied through the bit line BL and the word line WL. Theresistance-change films 30 in the low resistance state transition to thehigh resistance state when a current of a certain value or more flowsthrough the bit line BL and the word line WL.

The resistance-change films 30 primarily contain an oxide containing atleast one chemical element selected from the group consisting of hafnium(Hf), zirconium (Zr), nickel (Ni), tantalum (Ta), tungsten (W), cobalt(Co), aluminum (Al), iron (Fe), manganese (Mn), chromium (Cr), andniobium (Nb).

For example, the resistance-change films 30 are films of materials suchas HfO₂, Al₂O₃, TiO₂, NiO, WO₃, Ta₂O₅ and the like.

In forming a memory cell array as described above, a stacked body inwhich plural layers of the word lines WL and the insulating layers 20are alternately stacked is formed. Note that, the material of the wordlines WL (word line material layers) is for example silicon layers towhich impurities are added and that have conductivity, metal layers, orsilicide layers.

Thereafter, in order to separate the word lines WL in the X direction,if the stacked body is processed in a line and space pattern by etching,an aspect ratio of the laminate bodies left in the line shapes becomeshigh, and there are cases in which the laminate bodies easily fall down.

Thus, in the embodiment, as will be described below, the stacked bodyincluding the word lines WL and the insulating layers 20 are preventedfrom being patterned in the line and space pattern.

FIGS. 4A to 6B are schematic plan views illustrating a method of formingthe memory cell array according to the first embodiment.

After having formed the global bit lines GBL and the selecting elementson the substrate that is not illustrated, the plural layers ofinsulating layers 20 and the word line material layers are alternatelystacked on the interlayer insulating layers 12 (illustrated in FIG. 3)as a base layer.

An uppermost layer of the stacked body is for example the insulatinglayer 20, and FIG. 4A illustrates a top surface 50 of the stacked body.

Next, as illustrated in FIG. 4B, a plurality of first holes 51 is formedon the stacked body. The first holes 51 are arranged in a matrix shapein the X direction and the Y direction.

The first holes 51 extend in the stacking direction of the stacked body,and lower ends of the first holes 51 reach the conductive layers 15illustrated in FIG. 3.

Next, as illustrated in FIG. 5A, the resistance-change films 30 areformed on inner walls of the first holes 51. The resistance-change films30 are formed for example by an ALD (Atomic Layer Deposition) method,and are formed on side walls of the first holes 51 at a substantiallyhomogenous and even film thickness. The film thickness of theresistance-change films 30 is for example a few nm. Thereafter, theresistance-change films 30 formed on bottom surfaces (top surfaces ofthe conductive layers 15) of the first holes 51 are removed byanisotropic etching such as an RIE method.

Next, a metal material or conductive silicon is embedded inside theresistance-change films 30 in the first holes 51, and as illustrated inFIG. 5B, the pillar-shaped bit lines BL are formed. Lower ends of thebit lines BL reach the conductive layers 15 illustrated in FIG. 3.

A periphery of each bit line BL is surrounded by the resistance-changefilm 30, and a periphery of each resistance-change film 30 is surroundedby the word lines WL and the insulating layers 20.

Next, in the stacked body, regions that are adjacent to theresistance-change films 30 in the Y direction are removed by etching.Due to this, as illustrated in FIG. 6A, second holes 52 are formedbetween the bit lines BL that are adjacent in the Y direction.

By the formation of the second holes 52, the stacked body is dividedinto a plurality in the X direction. That is, the word lines WL of thestacked body are processed into line-shaped word lines WL that areseparated in the X direction and extend in the Y direction.

The second holes 52 extend in the stacking direction of the word linesWL, and lower ends of the second holes 52 reach the interlayerinsulating films 12 illustrated in FIG. 3.

Further, by the etching that forms the second holes 52, theresistance-change films 30 that were provided on both side walls of thebit lines BL in the Y direction can also be removed.

Note that, the resistance-change films 30 that were provided on the bothside walls of the bit lines BL in the Y direction may remain dependingon etching conditions and materials.

After the second holes 52 have been formed, the pillar-shaped bit linesBL are aligned in the Y direction between the laminate bodies that areadjacent in the X direction, with the second holes 52 being interposedbetween the bit lines BL.

The laminate bodies are not processed in the line and space pattern, andthe resistance-change films 30 and the pillar-shaped bit lines BL areprovided in contact with the laminate bodies in between the laminatebodies that are adjacent in the X direction.

Accordingly, the laminate bodies that are divided in the X direction aresupported by the resistance-change films 30 and the pillar-shaped bitlines BL being sandwiched between the laminate bodies that are adjacentin the X direction, and a possibility of fall-down is low.

As illustrated in FIG. 6B, the inter-bit line insulating films 21 areembedded in pillar shapes within the second holes 52.

Next, FIGS. 7A to 8B are schematic plan views illustrating a method offorming a memory cell array according to a second embodiment.

After having formed global bit lines GBL and selecting elements on asubstrate that is not illustrated, layers of insulating layers 20 andword line material layers are alternately stacked on interlayerinsulating layers 12 (illustrated in FIG. 3) as a base layer.

An uppermost layer of a stacked body is for example the insulating layer20, and FIG. 7A illustrates a top surface 50 of the stacked body.

Next, as illustrated in FIG. 7A, first holes 51 are formed on thestacked body. The first holes 51 are arranged in a matrix shape in an Xdirection and a Y direction.

The first holes 51 extend in a stacking direction of the stacked body,and lower ends of the first holes 51 reach the interlayer insulatingfilms 12 illustrated in FIG. 3.

As illustrated in FIG. 7B, inter-bit line insulating films 21 areembedded in pillar shapes in the first holes 51.

Next, in the stacked body, regions that are adjacent to the inter-bitline insulating films 21 in the Y direction are removed by etching. Dueto this, as illustrated in FIG. 8A, second holes 52 are formed betweenthe inter-bit line insulating films 21 that are adjacent in the Ydirection.

By the formation of the second holes 52, the stacked body is dividedinto a plurality in the X direction. That is, the word lines WL areprocessed into line-shaped word lines WL that are separated in the Xdirection and extend in the Y direction.

The second holes 52 extend in the stacking direction of the word linesWL, and lower ends of the second holes 52 reach conductive layers 15illustrated in FIG. 3.

After the second holes 52 have been formed, the pillar-shaped inter-bitline insulating films 21 are aligned in the Y direction between thelaminate bodies that are adjacent in the X direction with the secondholes 52 being interposed between the inter-bit line insulating films21.

The laminate bodies are not processed in a line and space pattern, andthe inter-bit line insulating films 21 are provided in contact with thelaminate bodies between the laminate bodies that are adjacent in the Xdirection.

Accordingly, the laminate bodies that are divided in the X direction aresupported by the pillar-shaped inter-bit line insulating films 21 beingsandwiched between the laminate bodies that are adjacent in the Xdirection, and a possibility of fall-down is low.

Next, as illustrated in FIG. 8B, resistance-change films 30 are formedon inner walls of the second holes 52. The resistance-change films 30are formed for example by an ALD method, and are formed on side walls ofthe second holes 52 at a substantially homogenous and even filmthickness. Thereafter, the resistance-change films 30 formed on bottomsurfaces (top surfaces of the conductive layers 15) of the second holes52 are removed by anisotropic etching such as an RIE method.

Next, a metal material or conductive silicon is embedded inside theresistance-change films 30 in the second holes 52, and pillar-shaped bitlines BL are formed. Lower ends of the bit lines BL reach the conductivelayers 15 illustrated in FIG. 3. As a result, a periphery of each bitline BL is surrounded by the resistance-change film 30.

Next, FIG. 9A to FIG. 10B are schematic plan views illustrating amodification of a method of forming a memory cell array of the secondembodiment.

In this specific example, as illustrated in FIG. 9A, corners of firstholes 51 are rounded. The corners of first holes 51 can be rounded by acontrol of etching conditions.

As illustrated in FIG. 9B, inter-bit line insulating films 21 areembedded in pillar shapes in the first holes 51. Corners of theinter-bit line insulating films 21 are also rounded in accordance withthe hole shapes.

Next, in a stacked body, regions that are adjacent to the inter-bit lineinsulating films 21 in a Y direction are removed by etching. Due tothis, as illustrated in FIG. 10A, second holes 52 are formed between theinter-bit line insulating films 21 that are adjacent in the Y direction.

The stacked body is divided into a plurality in the X direction. Thatis, word lines WL are processed into line-shaped word lines WL that areseparated in the X direction and extend in the Y direction.

The inter-bit line insulating films 21 are provided in contact with thelaminate bodies between the laminate bodies that are adjacent in the Xdirection. Accordingly, the laminate bodies that are divided in the Xdirection is supported by the pillar-shaped inter-bit line insulatingfilms 21 being sandwiched between the laminate bodies that are adjacentin the X direction, and a possibility of fall-down is low.

Since the corners of the inter-bit line insulating films 21 are rounded,portions of the second holes 52 that become adjacent to the inter-bitline insulating films 21 are thereby curved. Due to this, a width of thesecond holes 52 in the Y direction becomes larger at their ends than attheir center portion in the X direction.

A width W1 of surfaces of the word lines WL exposed by the second holes52 in the Y direction is larger than a width W2 at the center portion ofthe second holes 52 in the X direction.

Next, as illustrated in FIG. 10B, resistance-change films 30 are formedon inner walls of the second holes 52. The resistance-change films 30are formed for example by an ALD method on side walls of the secondholes 52 at a substantially homogenous and even film thickness.Thereafter, the resistance-change films 30 formed on bottom surfaces(top surfaces of conductive layers 15) of the second holes 52 areremoved by anisotropic etching such as an RIE method.

Next, a metal material is embedded inside the resistance-change films 30in the second holes 52, and pillar-shaped bit lines BL are formed. Eachresistance-change film 30 continuously surrounds an outer peripheralwall of each of the pillar-shaped bit lines BL.

An outer shape of the resistance-change films 30 and an outer shape ofthe bit lines BL reflect an outer shape of the second holes 52.

Accordingly, a width of the bit lines BL in the Y direction becomeslarge at their ends than at their center portion in the X direction. Anarea of the bit lines BL at portions facing the word lines WL via theresistance-change films 30 becomes large, and a forming voltage forforming a conduction path called a filament in the resistance-changefilms 30 can be reduced. It is possible to reduce the forming voltage,then it is possible to suppress defects from being generated in theresistance-change films 30.

Further, sidewall portions 30 a of the resistance-change films 30provided between the bit lines BL and the inter-bit line insulatingfilms 21 are curved. Sidewall portions of the bit lines BL makingcontact with the curved sidewall portions 30 a of the resistance-changefilms 30 are also curved.

In the resistance-change films 30, a length of the sidewall portions 30a can be made long by curving the sidewall portions 30 a extending inthe X direction and provided so as to connect the adjacent word linesWL. As a result, a leak current flowing via interfaces of the sidewallportions 30 a between adjacent memory cells in the X direction can besuppressed.

In the first embodiment, the second holes 52 illustrated in FIG. 6A canbe formed for example by the RIE (Reactive Ion Etching) method using amask having a plurality of openings. That is, a mask having openingscorresponding to relevant portions of the second holes 52. The stackedbody under the openings of the mask is removed by etching.

Further, the second holes 52 can alternatively be formed by the RIEmethod using a mask having opening grooves extending in the Y direction.That is, a mask having opening grooves corresponding to relevantportions between laminate bodies that are adjacent in the X direction.Even by using such a mask having the opening grooves, the second holes52 can be formed if an etching ratio of the bit lines BL and theresistance-change films 30 is differ from an etching ratio of the wordlines WL and the insulating layers 20.

Here, for example, as illustrated in FIG. 11A, if positions of edges ofmask opening grooves extending in the Y direction are positioned on abit line BL side than ends of the resistance-change films 30 in the Xdirection, the width of the second holes 52 in the X direction becomessmaller than the widths of the bit lines BL and the resistance-changefilms 30 in the X direction of the stacked body.

That is, a width Wa of portions of the word lines WL adjacent to thesecond holes 52 becomes larger than a width Wb of the word lines WLadjacent to the bit lines BL.

Accordingly, sidewalls of the word lines WL along the Y direction areformed in a concavo-convex pattern. As a result, a resistance of theword lines WL can be made low. Note that, the ends of the word lines WLexposed by the second holes 52 are positioned on a center side of thebit lines BL than boundaries of the bit lines BL and theresistance-change films 30, so that the resistance-change films 30between the bit lines BL and the word lines WL are not etched. In otherwords, the width Wb−width Wa is larger than the film thickness of theresistance-change films 30.

As for the second embodiment, similarly, the second holes 52 illustratedin FIG. 8A can be formed for example by the RIE method using the maskhaving the opening grooves extending in the Y direction.

The stacked body under the opening grooves of the mask is removed byetching.

Here, for example, as illustrated in FIG. 11B, if positions of edges ofthe mask opening grooves extending in the Y direction are positioned topartially overlap with the inter-bit line insulating films 21, the widthof the second holes 52 in the X direction becomes smaller than the widthof the inter-bit line insulating films 21 in the X direction.

That is, a width Wa of portions of the word lines WL adjacent to thesecond holes 52 becomes larger than a width Wb of the word lines WLadjacent to the inter-bit line insulating films 21.

Accordingly, sidewalls of the word lines WL along the Y direction areformed in a concavo-convex pattern. As a result, a resistance of theword lines WL can be made low.

While certain embodiments have been described, these embodiments havebeen presented by way of example only, and are not intended to limit thescope of the inventions. Indeed, the novel embodiments described hereinmay be embodied in a variety of other forms; furthermore, variousomissions, substitutions and changes in the form of the embodimentsdescribed herein may be made without departing from the spirit of theinventions. The accompanying claims and their equivalents are intendedto cover such forms or modifications as would fall within the scope andspirit of the invention.

What is claimed is:
 1. A semiconductor memory device comprising: wordlines arranged in a first direction, extending in a second directionintersecting with the first direction, and stacked above a base layer ina third direction intersecting with the first direction and the seconddirection, the word lines including a first word line and a second wordline being adjacent to the first word line in the first direction;insulating layers stacked with the word lines interposed in the thirddirection; pillars consisting of a same conductive material aligned inthe second direction between the first word line and the second wordline, the pillars extending in the third direction and including a firstpillar and a second pillar being adjacent to the first pillar in thesecond direction; a data storage film provided between one of the firstand second pillars and one of the first and second word lines; and aninter-pillar insulating film provided between the first pillar and thesecond pillar, the pillars each having a center part and lateral partsintegrally formed of said same conductive material, the lateral partssandwiching the center part in the first direction and being closer tothe first word line and the second word line respectively, and thecenter part having a maximum width in the second direction narrower thanmaximum widths in the second direction of the lateral parts.
 2. Thedevice according to claim 1, wherein the data storage film includes aresistance-change portion.
 3. The device according to claim 1, whereinthe data storage film is a part of a film surrounding the one of thefirst and second pillars.
 4. The device according to claim 3, whereinthe film surrounding the one of the first and second pillars includes acurved part between the one of the first and second pillars and theinter-pillar insulating film.
 5. The device according to claim 4,wherein the one of the first and second pillars has a curved lateralsurface that is in contact with the curved part.
 6. The device accordingto claim 1, wherein the one of the first and second word lines has arecessed portion that faces the one of the first and second pillars. 7.The device according to claim 6, wherein the data storage film isprovided in the recessed portion.